1. Field of the Invention
The present invention relates to a noninvasive sphygmomanometer, and more particularly to the sphygmomanometer providing a function for correcting a measurement error according to a difference in arm circumference lengths of subject persons.
2. Description of the Related Art
Conventionally, the most general method for noninvasively measuring a blood pressure value is a method for interrupting bloodstream to peripheral regions by bringing pressure from outside to regions where arteries pass such as arms, wrists, or the like of a subject person and thereafter for observing Korotkoff sounds or a change of pulsation in the arteries during a process to gradually reduce the brought pressure, thereby measuring the blood pressure value.
Furthermore, to bring the pressure to the region where the arteries pass is conducted by winding an armband with a bladder as a bag to contain air therein on the region where the arteries pass and by applying and reducing pressure in the bladder from outside, and this controls interrupting and reopening the bloodstream to the peripheral regions.
However, this method is lower in measurement accuracy compared with an invasive method for directly measuring pressure in a blood vessel. The reason for this is that results of blood pressure measurement are different depending on an arm circumference length of the subject person or a size of the bladder for use. For example, when a width (a direction perpendicular to a direction of winding the armband) of the bladder is much shorter than the arm circumference length of the subject person, blood pressure is detected higher than an actual value; and reversely, when the width thereof is much longer, the blood pressure is detected lower than the actual value. Similarly, when a length (the direction of winding the armband) of the bladder is much shorter than the arm circumference length of the subject person, the blood pressure is detected higher than the actual value; and reversely, when the length thereof is much longer, the blood pressure is detected lower than the actual value. Therefore, it is ideal to prepare the bladders corresponding to all subject persons in order to obtain an accurate blood pressure value. However, it is difficult to actually commercialize and prepare them in a medical setting or the like if cost reduction, securement of space, needs of the accurate blood pressure value of the subject person, and the like are compared and considered.
Accordingly, considering a range of the arm circumference length where measurement errors are within a certain range as a range of a suitable arm circumference length of the bladder, plural armbands having different bladder sizes are often prepared in order to cover the range of the arm circumference length of the subject person which can be previously estimated. In actual measurement, the armband is selected by (1) measuring the arm circumference length of the subject person using a tape measure, or (2) by a hunch of a measuring person.
However, in the method (1), measurement with the tape measure is a time-consuming work; furthermore, there is a problem that the tape measure must be found out if the tape measure is not available at a site where measurement is taken place. Furthermore, in the method (2), there is a problem of an error in selection of the armband due to the hunch by the measuring person, resulting in lacking in accuracy.
Therefore, methods with accuracy and with little time-consuming work are disclosed. Specifically, (3) a method for marking the armband with a scale showing the arm circumference length (for example, refer to Utility Model 1), (4) a method for providing a display of a suitable range of the arm circumference length with the armband (for example, refer to Utility Model 1), (5) a method for providing a measurer of the arm circumference length with the armband, for example, an electric position detector such as a variable resistor or the like with the armband (for example, refer to Patent Document 2), and (6) a method for estimating the arm circumference length from a time required for applying pressure (for example, refer to Patent Document 2), specifically, a method for measuring the pressure in the bladder while applying pressure, and for estimating the arm circumference length of the subject person based on a time required for reaching a predetermined pressure value or a time required for reaching from the predetermined pressure value to a predetermined pressure value higher than therefrom, are disclosed.
[Patent Document 1]
Japanese Utility Model Laid-open No. Sho 62-152702 (FIG. 1 to FIG. 5)
[Patent Document 2]
Japanese Patent Laid-open No. Hei 6-245911 (Page 2, FIG. 2)
However, the aforementioned methods (3) to (6) have following problems.
In the method (3), whether or not a size of the bladder in the armband is appropriate for the subject person is determined from a scale value when the armband is wound on an arm of the subject person, and a correction of the blood pressure value to be measured is possible based on the scale value, and meanwhile, whether the bladder is appropriate or not is determined only after it is wound. Therefore, there is a problem that the bladder must be wound again in order to change the armband having a bladder of a different size if the bladder is not appropriate.
Furthermore, in order to take a measurement more accurately, a method for calculating the blood pressure value taking the measured arm circumference length into consideration is thought. However, in this case, there is a problem that the correction of the blood pressure value must be made by people, or that the arm circumference length must be directly inputted using an operation button of a sphygmomanometer.
In the method (4), as well as the method (3), there is a problem that the armband must be wound again because whether or not the bladder is appropriate is determined only after the armband is wound.
In the method (5), the accurate blood pressure value is obtained without winding the armband again. However, there is a problem that not only a structure of the armband is complicated but also a cost is increased and also and defective goods and failure are likely to be generated more often.
In the method (6), there is a problem that the estimated arm circumference length is largely changed according to strength of winding the armband.